HONG KONG - Tens of thousands of people marched on Hong Kong's parliament on Sunday to demand the scrapping of proposed extradition rules that would allow people to be sent to mainland China for trial - a move which some fear puts the city's core freedoms at risk.

Opponents of the proposal fear further erosion of rights and legal protections in the free-wheeling financial hub - freedoms which were guaranteed under the city's handover from British colonial rule to Chinese sovereignty in 1997.

Ranks of marchers snaked peacefully for more than three hours through the shopping and business districts of Causeway Bay and Wanchai, with thousands staying on into the evening outside the Legislative Council and government headquarters.

Police said 22 800 people marched at the peak of the procession, but organisers estimated 130 000 turned out - making it one of the largest street protests in the city for several years.

Observers said the turnout dwarfed an earlier protest against the plan last month.

"Hong Kong people and visitors passing by Hong Kong will lose their right not to be extradited into mainland China," he said. "They would need to face an unjust legal system on the mainland."

Some younger marchers said they were worried about travelling to the mainland after the move, which comes just as the government encourages young people to deepen ties with the mainland and promotes Hong Kong's links with southern China.

Law clerk Edward Wen, 45, said the difference in human rights standards between Hong Kong and the mainland was too great to bridge.

"You will be screwed as long as they put up a crime on your behalf," he said.

The marchers' chanted demands for Hong Kong Chief Executive Carrie Lam to step down echoed through the high-rise streets, with some protesters saying she had "betrayed" Hong Kong.

Some sported yellow umbrellas - the symbol of the Occupy pro-democracy movement that paralysed parts of Hong Kong for 11 weeks in 2014.

The proposed changes have sparked an unusually broad chorus of concern from international business elites to lawyers and rights' groups and even some pro-establishment figures.

Chris Patten, the last British governor of Hong Kong who handed the city back to Chinese rule in 1997, on Saturday described the move as "an assault on Hong Kong's values, stability and security", government-funded broadcaster RTHK reported.

LOOPHOLES

Chief Executive Lam and other government officials are standing fast by their proposals, calling them vital to plug long-standing loopholes.

Under the changes, the Hong Kong leader would have the right to order the extradition of wanted offenders to China, Macau and Taiwan as well as other countries not covered by Hong Kong's existing extradition treaties.

As a safeguard, such orders, to be issued case-by-case, could be challenged and appealed through the city's vaunted legal system.

Government officials have said no one at risk of the death penalty or torture or facing a political charge could be sent from Hong Kong. Under pressure from local business groups, they earlier exempted nine commercial crimes from the new provisions.

The proposals could be passed into law later in the year, with the city's pro-democratic camp no longer holding enough seats to block the move.

The government has justified the swift introduction of the changes by saying they are needed so a young Hong Kong man suspected of murdering his girlfriend in Taiwan can be extradited to face charges there.

The government's assurances are not enough for Lam Wing-kee, a former Hong Kong political bookseller who said in 2016 he was abducted by mainland agents in the city.

Lam left Hong Kong for Taiwan last week, saying he feared being sent back to the mainland under the new laws and his experience showed he could have no trust in China's legal system.

A group of 33 followers of Falun Gong, a religious sect banned in China, flew from Taiwan to Hong Kong on Saturday to join the march but were refused entry to Hong Kong, RTHK reported.